1. Field of the Invention
This invention relates to non-contact counters for counting the number of objects in a stack. The invention has particular utility for counting relatively irregular stacked objects, such as stuffed mailing envelopes
2. Description of Related Developments
Bulk mailing operations require highly accurate accounting of objects being mailed for job control and billing purposes. Such counts are especially important when mailing credit cards because of the need to maintain security against unauthorized use of such cards In a typical mailing operation for credit cards, several thousand cards per day are mailed as replacements to existing customers or new cards to new customers At such volumes, manual counting of the cards is expensive and unreliable. To accomplish fast and accurate counting of credit cards, highly accurate card counters have been developed. In general, these counters scan one of the edges of a stack of cards and count them by sensing momentary differences in reflected light intensity between the card edges and the space between cards. U.S. Pat. Nos. 27,869, 3,790,759, 3,813,523, 4,373,135, 4,771,443 and 4,912,317 disclose such card counters While such systems provide fast and accurate counting of stacks of credit cards, that have well defined, substantially uniform edges which can be arranged in a highly regular, coplanar fashion, such systems do not provide a means for counting irregularly shaped objects, such as stuffed envelopes. Thus, in a typical credit card bulk mailing process, a cost effective machine counting of the cards can be maintained only up until the point that the cards are loaded or stuffed into envelopes. Thereafter, accountability for the cards by counting of the loaded envelopes becomes a much slower, more expensive, and more unreliable part of the accountability system. This is so because the loaded envelopes are irregular in shape and do not present a uniform, substantially planar edge array that yields a signal of sufficient quality to be used for counting purposes.
One system for counting stacks of bound booklets is illustrated in Japanese Published Patent Application 61-272892. In this design, to improve the accuracy of the count, a vibrating stacker is used for aligning up the booklets on a booklet stand prior to counting. Such an arrangement involves expense in the design and control of the vibrating stand and unnecessary delays in counting. Moreover, booklets are of substantially uniform thickness and can give a relatively uniform signal response to detection. Such as system is less useful for counting a stack of envelopes of varying thickness, for example, ones that contain differing numbers of credit cards.